Astringent

A crystal of alum, an astringent

An astringent (occasional alternative: adstringent) substance is a chemical compound that tends to shrink or constrict body tissues. The word "astringent" derives from Latin adstringere, meaning "to bind fast". Two common examples are calamine lotion and witch hazel. Another example is yerba mansa, a native plant of California.^[1]

Astringency is also the dry, puckering mouthfeel caused by tannins found in many fruits such as blackthorn (sloe berries), Aronia chokeberry, chokecherry, bird cherry, quince and persimmon fruits, and banana skins. The tannins (which are types of polyphenols) bind the salivary proteins, causing them to precipitate or aggregate^[2] and lead to a rough "sandpapery" or dry sensation in the mouth. Tannins are found in some red wines and teas. A small amount of astringency is expected in some wines, especially young red wines made from grapes such as cabernet sauvignon and merlot.

Uses

Astringents in medicine cause constriction or contraction of mucous membranes or exposed tissues and are often used internally to check discharge of blood serum or mucous secretions.^[3] This can happen with a sore throat, hemorrhages, diarrhea, or with peptic ulcers. Externally applied astringents, which cause mild coagulation of skin proteins, dry, harden, and protect the skin.^[4] People with acne are often advised to use astringents if they have oily skin.^[5] Mild astringent solutions are used in the relief of such minor skin irritations as those resulting from superficial cuts, allergies, insect bites,^[4] or fungal infections such as athlete's foot.^[6]

Some common astringent agents include alum, acacia, sage,^[7] yarrow,^[8] witch hazel, bayberry, distilled vinegar, very cold water, and rubbing alcohol. Astringent preparations include silver nitrate, potassium permanganate, zinc oxide, zinc sulfate, Burow's solution, tincture of benzoin, and vegetable substances such as tannic and gallic acids. Balaustines are the red rose-like flowers of the pomegranate, which are very bitter to the taste. In medicine, their dried form has been used as an astringent.^[9] Some metal salts and acids have also been used as astringents.^[10] Redness-reducing eye drops contain an astringent. In the past, Goulard's Extract was used, but is now discontinued.

References

1. Anemopsis californica from University of California, Irvine
2. Fennema, Food Chemistry, 4th Ed., page 656
3. Brodin, Michael (1998). The Over-The-Counter Drug Book. Simon and Schuster. p. 382. ISBN 978-0-671-01380-6. Retrieved 4 June 2014.
4. Peter A. Ciullo (31 December 1996). Industrial Minerals and Their Uses: A Handbook and Formulary. William Andrew. p. 407. ISBN 978-0-8155-1808-2. Retrieved 4 June 2014.
5. Acne from http://www.brown.edu
6. Dockery, Gary L.; Crawford, Mary Elizabeth (1999). Color Atlas of Foot and Ankle Dermatology. Lippincott Williams & Wilkins. p. 171. ISBN 978-0-397-51519-6. Retrieved 4 June 2014.
7. Dorland, W. A. Newman (1907). The american illustrated medical dictionary (4th ed.). Philadelphia and London: W.B. Saunders company. pp. 14, 39, 635. Retrieved 4 June 2014.
8. Grieve, Maud (1 June 1971). A Modern Herbal: The Medicinal, Culinary, Cosmetic and Economic Properties, Cultivation and Folk-lore of Herbs, Grasses, Fungi, Shrubs, & Trees with All Their Modern Scientific Uses. Dover Publications. pp. 863–864. ISBN 978-0-486-22799-3. Retrieved 4 June 2014.
9. History of Science: Cyclopædia, or, An universal dictionary of arts and sciences…
10. Gregory, James (1833). Conspectus medicinae theoreticae: a view of the theory of medicine; in two parts: Part I. Containing physiology and pathology. Part II. Containing therapeutics (2nd ed.). London: Stirling & Kenneg. pp. 255–256. Retrieved 4 June 2014.